Oxidation process



United States Patent O OXIDATION PROCESS Chester S. Morgan, Jr., Corpus Christi, Tex., and Nat C. Robertson, Cambridge, Mass, assignors to Celanese Corporation of America, New York, N. Y., a corporation of Delaware No Drawing. Application June 30, 1951, Serial No. 234,657

12 Claims. (Cl. 260-451) This invention relates to the production of organic compounds and relates more particularly to the production of aliphatic organic compounds by the catalytic liquid phase oxidation of lower aliphatic hydrocarbons.

An object of this invention is the provision of an improved process for the catalytic liquid phase oxidation of lower aliphatic hydrocarbons.

Another object of this invention is the provision of an improved process for the catalytic liquid phase oxidation of lower aliphatic hydrocarbons in which process the extent of oxidation may be elfectively controlled.

A further object of this invention is to provide a process for the catalytic liquid phase oxidation of lower aliphatic hydrocarbons whereby improved yields of esters and ketones may be obtained.

Other objects of this invention will appear from the following detailed description.

The direct oxidation of aliphatic hydrocarbons such as propane, butane, iso-butane, pentane, etc. or mixtures of these hydrocarbons, with air or oxygen to obtain alcohols aldehydes, ketones, acids, etc. has been the subject of considerablestudy and a substantial amount of research has gone into developing commercially feasible hydrocarbon oxidation processes. Although many processes for the liquid phase oxidation of the aliphatic hydrocarbons mentioned above have been proposed, few, if any, have been commercially successful. On the other hand, the oxidation of said aliphatic hydrocarbons wherein the oxidation is carried out in the vapor phase has been highly successful and now constitutes a major source of many valuable organic chemicals.

However, processes forthe liquid phase oxidation of such aliphatic hydrocarbons are very attractive from the point of view that they do not consume as much heat as vapor phase operations and, in addition, do not generally form as great a variety of products. In order to improve liquid phase oxidation operations to the end that they may be employed for commercial operation, various expedients have been suggested. It has been proposed that various liquids, such as acetic acid, propionic acid, butyric acid, iso-ibutyric acid, etc., be employed as solvents for the aliphatic hydrocarbon during the oxidation reaction. The use of various catalysts, such as finely divided metals or the organicor inorganic acid salts of the metals, has also been mentioned as a means whereby lower and more effective reaction temperatures may be employed. The advantage of lower reaction temperatures lies in the production of greater yields and more effective utilization of the hydrocarbon raw material. The catalytic liquid phase oxidation of aliphatic hydrocarbons, particularly straight chain hydrocarbons, has been found to yield a product mixture which contains predominant amounts of acetic acid. Study of the reaction has indicated that the latter comprises the ultimate or end product of the oxidation of the .intermediate products which are formed, which intermediate products include both esters and ketones. Thus, in order to obtain higher yields of esters and ketones, the reaction should be halted before said intermediate compounds undergo further oxidation. As a process step, the haltingof the reaction after a specific degree of oxidation has taken place is not particularly practical since the reaction is very complex and all of the several oxidation reactions takeplace simultaneously. Up to the present time, there has been developed no satisfactory method of controlling the catalytic liquid phase oxidation of aliphatic hydrocarbons in order to increase the recovery of the intermediate oxidation products.

We have now found that if the catalytic oxidation of lower aliphatic hydrocarbons is carried out in the liquid phase, in the presence of a solvent and employing a mixed oxidation catalyst consisting of both a catalytic metal compound and 2 to 20% on the weight of the solvent of an alkali metal or alkaline earth metal compound, the further oxidation of the intermediate ester and ketone oxidation products is strongly inhibited. Since the further oxidation of said compounds is inhibited by the use of said mixed catalyst, a substantially increased recovery of said intermediate esters and ketones is obtained with a corresponding decrease in the amount of acetic acid produced. This result is quite surprising since the alkali metal and alkaline earth metal compounds have been considered to be oxidation promoters or initiators when employed in connection with other metal oxidation catalysts in liquid phase hydrocarbon oxidation operations and, especially, when said alkali metal or alkaline earth metal compounds are present in small amounts, e. g. less than 1% on the weight of the solvent. Ordinarily, it would be expected that an increase in the concentration of said added alkali metal and alkaline earth metal catalyst would not further to increase the initiator or promoter activity of said materials. As we have now discovered, however, an increase in the amount of alkali metal or alkaline earth metal employed, within'a specific range of concentrations, acts to cause said alkali metal and alkaline earth metal compounds to function as reaction inhibitors or moderators.

As examples of the oxidation catalysts which may be employed in carrying out liquid phase hydrocarbon oxidation reactions, there may be mentioned the salts of metals such as cobalt, nickel, copper, cerium, iron, mercury, chromium, antimony, manganese, uranium, molybdenum, tungsten, tantalum, columbium, vanadium, zirconium, titanium, lead, tin, gold and silver, and particularly, the salts of said metals with organic acids such as, for example, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, benzoic acid and naphthenic acid.

The alkali metal and alkaline earth metal moderators which may be employed may be, for example, the sodium, potassium, magnesium, barium, calcium or strontium salts or organic acids such as formic acid, acetic acid, propionic acid, butyric acid or isobutyric acid. Examples of other compounds which may also be employed are the alkali metal or alkaline earth metal salts of hydrocyanic acid, boric acid, etc. In some instances the weak acid salts of strong bases, such as tetramethyl ammonium hydroxide, may also be usefully employed as catalyst moderators. As brought out above, the alkali metal and alkaline earth metal catalyst moderators must be present in amounts of 2 to 20% on the weight of the solvent which is employed in the liquid phase aliphatic hydrocarbon oxidation process in order to attain the desired moderating effect.

The catalytic liquid phase oxidation of the lower aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane, etc. is carried out most advantageously at temperatures of to 225 C. and under pressures of 200 to 2000 pounds per square inch absolute, employing air, oxygen or oxygen diluted with any suitable inert gas, as the oxidizing agent. As a solvent for the hydrocarbon undergoing oxidation, we have found that acetic acid is most suitable when oxidizing propane or n-butane although other oxidation-resistant solvents such as propionic acid, butyric acid, Valerie acid, methyl acetate, ethyl acetate, benzene, diphenyl or mixtures containing any two or more of these solvents in any proportion may aiso be employed.

While the liquid phase catalytic oxidation of said lower aliphatic hydrocarbons may be carried out in batch-wise operations, it is preferably carried out in a continuous manner. Thus, a suitable reaction vessel may be charged with the solvent to be employed, the desired catalyst mixture added to the solvent in a predetermined amount, and the hydrocarbon and oxidizing gas then introduced at the desired, controlled rate while maintaining the temperature and pressure within the above-mentioned ranges. The reaction conditions employed are preferably such that the oxygen introduced into the reactor will be consumed completely by the formation of oxygenated reac tion products. Accordingly, the gaseous residue of the oxidation reaction will ordinarily be free of unreacted oxygen.

In order to condense the overhead vapors from the oxidation reaction, a condenser is provided which is maintained at a temperature which is sufiiciently low to ensure the condensation of all of the condensable components in the vapors. The use of a condenser temperature of to 120 C., say 10 C., gives satisfactory results. The overhead vapors comprise water, unreacted hydrocarbon and hydrocarbon oxidation products. The fixed gases, such as nitrogen and carbon dioxide are vented to the atmosphere and any uncondensed watersolubles are absorbed in a suitable water absorber. The condensate is permitted to settle out into two phases, an upper hydrocarbon phase and a lower aqueous phase. The reaction products present partition between the phases. The aqueous phase comprises the water of reaction and a portion of the watersoluble oxidation products. The remainder of the oxidation products which distill over dissolve in the hydrocarbon phase. The aqueous phase is subjected to suitable treatment to recover the oxidation products dissolved therein. The hydrocarbon phase, without any treatment to separate the oxidation products which are present therein is returned directly to the reactor where the unreacted hydrocarbon undergoes further oxidation. in some instances, the hydrocarbon phase may be treated to separate some of the oxidation products prior to returning the hydrocarbon phase to the reactor.

The volumetric ratio of oxygen to hydrocarbon introduced into the system is generally maintained at from about 0.5 to 10 volumes of oxygen for each volume of additional hydrocarbon introduced, the respective volumes being calculated at standard conditions of temperature and pressure, i. e. 0 C. and 760 mm. The recycled hydrocarbon may be from to 50 parts by weight for each part by weight of fresh hydrocarbon introduced.

in order further to illustrate the novel process of our invention, the following example is given:

Example 384 parts by Weight of glacial acetic acid, 0.3% by weight of cobalt acetate and 26 parts by weight (6.7% by weight based on the acid) of sodium acetate are charged to a stainless steel reactor having an inlet for air and hydrocarbon feed and an outlet for vaporized oxidation products. Liquid n-butane is introduced into the reactor at a rate of 0.6 part by Weight per minute together with air, in the form of finely-divided bubbles, at a rate of 1.285 parts by weight per minute. The reactor is maintained under a pressure of 815 pounds per square inch absolute and the reaction mixture at a temperature of 160 to 165 C. Under these conditions the reaction of the oxygen is complete. The overhead vapors and inert gases from the reactor are chilled in a condenser maintained at about 45 C. and a condensate consisting of a lighter hydrocarbon phase and a dense aqueous phase is obtained. The uncondensed nitrogen is vented. The dense aqueous phase is withdrawn intermittently from a decanter while the lighter hydrocarbon phase is returned to the reactor. After operating for 11 hours, a material balance on the system indicates that for every 100 parts by weight of n-butane reacted a yield of 46 parts by weight of free acetic acid, 46 parts by weight of ethyl acetate, 22.6 parts by weight of methyl ethyl ketone and 4.5 parts by weight of alcohols is obtained. Under the same reaction conditions but without employing sodium acetate as the catalyst moderator, the yield obtained, for each 100 parts by weight of n-butane reacted, is 61 parts by weight of free acetic acid, 26.5 parts by weight of ethyl acetate, 12.8 parts by weight of methyl ethyl ketone and 2.3 parts by weight of alcohol.

it is to be understood that the foregoing detailed description was given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention what we desire to secure by Letters Patent is:

1. Process for the production of oxygenated organic compounds. which comprises oxidizing an aliphatic hydrocarbon by passing an oxygen-containing gas through a reaction mixture comprising a solution of said hydrocarbon in an oxidation-resistant solvent therefor under conditions of elevated temperature and superatmospheric pressure to cause the oxidation reaction to proceed, said 3;

solution containing both a catalyst favoring the oxidation of said hydrocarbon and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts.

2. Process for the production of oxygenated organic compounds, which comprises oxidizing an aliphatic hydrocarbon by passing an oxygen-containing gas through a reaction mixture comprising a solution of said hydrocarbon in an oxidation-resistant solvent therefor under conditions of elevated temperature and superatmospheric pressure to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said hydrocarbon and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts, allowing part of said reaction mixture including water of reaction and other oxidation products to distill over, condensing the distillate to yield an aqueous phase and a hydrocarbon phase, and separating the hydrocarbon phase from the aqueous phase and returning it to the reaction.

3. Process for the production of oxygenated organic compounds, which comprises oxidizing an aliphatic hydrocarbon by passing an oxygen-containing gas through a reaction mixture comprising a solution of said hydrocarbon in an oxidation-resistant aliphatic acid solvent therefor under conditions of elevated temperature and superatmospheric pressure to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said hydrocarbon and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts.

4. Process for the production of oxygenated organic compounds, which comprises oxidizing an aliphatic hydrocarbon by passing an oxygen-containing gas through a reaction mixture comprising a solution of said hydrocarbon in an oxidation-resistant aliphatic acid solvent therefor under conditions of elevated temperature and superatmospheric pressure to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said hydrocarbon and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts, allowing part of said reaction mixture including water of reaction and other oxidation products to distill over, condensing the distillate to yield an aqueous phase and a hydrocarbon phase, and separating the hydrocarbon phase from the aqueous phase and returning it to the reaction.

5. Process for the production of oxygenated organic compounds, which comprises oxidizing an aliphatic hydrocarbon by passing an oxygen-containing gas through a reaction mixture comprising a solution of said hydrocarbon in an oxidation-resistant solvent therefor while maintaining the same at a temperature of to 225 C. and under a pressure of 200 to 2000 pounds per square inch absolute to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said hydrocarbon and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the Weight of the solvent of a salt of a strong base and weak acid. said salt being selected from the group consisting of alkali metal salts. alkaline earth metal salts and quaternary ammonium hydroxide salts.

.6. Process for the production of oxygenated organic compounds, which comprises oxidizing an aliphatic hydrocarbon by passing an oxygen-containing gas through a reaction mixture comprising a solution of said hydrocarbon in an oxidation-resistant solvent therefor while maintaining the same at a temperature of 125 to 225 C. and under a pressure of 200 to 2000 pounds per square inch absolute to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said hydrocarbon and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts, allowing part of said reaction mixture including water of reaction and other oxidation products to distill over, condensing the distillate to yield an aqueous phase and a hydrocarbon phase, and separating the hydrocarbon phase from the aqueous phase and returning it to the reaction.

7. Process for the production of oxygenated organic compounds, which comprises oxidizing an aliphatic hydrocarbon by passing an oxygen-containing gas through a reaction mixture comprising a solution of said hydrocarbon in an oxidation-resistant aliphatic acid solvent therefor while maintaining the same at a temperature of 125 to 225 C. and under a pressure of 200 to 2000 pounds per square inch absolute to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said hydrocarbon and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and Weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts, allowing part of said reaction mixture including water of reaction and other oxidation products to distill over, condensing the distillate to yield an aqueous phase and a hydrocarbon phase, and separating the hydrocarbon phase from the aqueous phase and returning it to the reaction.

8. Process for the production of oxygenated organic compounds, which comprises oxidizing butane by pass ing an oxygen-containing gas through a reaction mixture comprising a solution of said butane in acetic acid under conditions of elevated temperature and superatmospheric pressure to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said butane, and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts.

9. Process for the production of oxygenated organic compounds, which comprises oxidizing butane by passing an oxygen-containing gas through a reaction mixture comprising a solution of said butane in acetic acid under conditions of elevated temperature and superatmospheric pressure to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said butane, and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2

to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts, allowing part of said reaction mixture including water of reaction and other oxidation products to distill over, condensing the distillate to yield an aqueous phase and a hydrocarbon phase, and separating the hydrocarbon phase from the aqueous phase and returning it to the reaction.

10. Process for the production of oxygenated organic compounds, which comprises oxidizing butane by passing an oxygen-containing gas through a reaction mixture comprising a solution of said butane in acetic acid while maintaining the same at a temperature of to 225 C. and under a pressure of 200 to 2000 pounds per square inch absolute to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidationof said butane, and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline eafth metal salts and quaternary ammonium hydroxide sa ts.

11. Process for the production of oxygenated organic compounds, which comprises oxidizing butane by passmg an oxygen-containing gas through a reaction mixture comprising a solution of said butane in acetic acid while maintaining the same at a temperature of 125 to 225 C. and under a pressure of 200 to 2000 pounds per square inch absolute to cause the oxidation reaction to proceed, said solution containing both a catalyst favoring the oxidation of said butane, and, as a moderator of the oxidation reaction to inhibit oxidation of intermediate ester and ketone oxidation products produced in said reaction, 2 to 20% on the weight of the solvent of a salt of a strong base and weak acid, said salt being selected from the group consisting of alkali metal salts, alkaline earth metal salts and quaternary ammonium hydroxide salts, allowing part of said reaction mixture including water of reaction and other oxidation products to distill over, condensing the distillate to yield an aqueous phase and a hydrocarbon phase, and separating the hydrocarbon phase from the aqueous phase and returning it to the reaction.

12. Process for the production of oxygenated organic compounds, which comprises forming a reaction mixture by adding butane to acetic acid containing 0.3% on the Weight of said acid of cobalt acetate and 6.7% on the weight of said acid of sodium acetate, passing an oxygen-containing gas through said reaction mixture while maintaining the same at a temperature of to C. and under a pressure of 200 to 2000 pounds per square inch absolute, allowing part of said reaction mixture including water of reaction and other oxidation products to distill over, condensing the distillate to yield an aqueous phase and a butane phase, separating the butane phase from the aqueous phase and returning it to the reaction.

Loder Dec. 9, 1941 Gerlicher Feb. 24, 1942 

1. PROCESS FOR THE PRODUCTION OF OXYGENATED ORGANIC COMPOUNDS WHICH COMPRISES OXIDIZING AN ALIPHATIC HYDROCARBON BY PASSING AN OXYGEN-CONTAINING GAS THROUGH A REACTION MIXTURE COMPRISING A SOLUTION OF SAID HYDROCARBON IN A OXIDATION-RESISTANT SOLVENT THEREFOR UNDER CONDITIONS OF ELEVATED TEMPERATURE AND SUPERATMOSPHERIC PRESSURE TO CAUSE THE OXIDATION REACTION TO PROCEED, SAID SOLUTION CONTAINING BOTH A CATALYST FAVORING THE OXIDATION OF SAID HYDROCARBON AND, AS A MODERATOR OF THE OXIDATION REACTION TO INHIBIT OXIDATION OF INTERMEDIATE ESTER AND KETONE OXIDATION PRODUCTS PRODUCED IN SAID REACTION, 2 TO 20% ON THE WEIGHT OF THE SOLVENT OF A SALT OF A STRONG BASE AND WEAK ACID, SAID SALT BEING SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL SALTS, ALKALINE EARTH METAL SALTS AND QUATERNARY AMMONIUM HYDROXIDE SALTS. 